1. Field of the Invention
The invention relates to processes for the production of oligomers from olefins, and more particularly relates to the production of oligomers from internal olefins by means of a boron trifluoride catalyst.
2. Description of Related Methods
Friedel-Crafts catalysts have long been known to oligomerize olefins. For example, see U.S. Pat. No. 3,410,925 to Eby, et al. in which olefins are mixed with alkylatable aromatic hydrocarbons over a Friedel-Crafts catalyst to form an alkylation sludge which is then mixed with olefins having 3 to 18 carbon atoms which are also passed over the catalyst to produce olefin dimers. U.S. Pat. No. 3,652,706 to Saines, et al. describes the polymerization of olefins having 2 to 20 carbon atoms over a Friedel-Crafts metal halide catalyst plus a hydrogen form of mordenite to produce compounds having a molecular weight between 700 and 2,500. Production of a gasoline fuel composition is described in U.S. Pat. No. 3,749,560 to Perilstein which occurs by reacting a mixture of mono olefins (greater than 50 weight percent alpha olefins) over a Friedel-Crafts catalyst heated to a temperature around 145.degree. C. to produce oligomers having molecular weights between 350 to 1,500. Also, U.S. Pat. No. 3,149,178 to Hamilton, et al. reveals an improved method for making polymerized olefin synthetic lubricants via a particular distillation technique of oligomers made from alpha mono olefins using a Friedel-Crafts catalyst. Alpha olefins having six to twelve carbon atoms may be dimerized in the presence of a Friedel-Crafts catalyst according to the method described in U.S. Pat. No. 4,172,855 to Shubkin, et al.
It is also known that the term "Friedel-Crafts catalysts" includes boron trifluoride among other metal halidetype Lewis catalysts, see Kirk-Othmer Encyclopedia of Chemical Technolology, Third Edition, Vol. 11, pg 292. Boron trifluoride has also been known to polymerize olefins, as seen in F. Albert Cotton, et al., Advanced Inorganic Chemistry: A Comprehensive Text, Interscience Publishers, 1962, p. 191.
A number of U.S. patents have also used BF.sub.3 to oligomerize olefins. Close study will reveal that alpha olefins are considered the only useful form. For example, U.S. Pat. No. 2,780,664 to Serniuk describes the reaction of conjugated dienes with mono alpha and internal olefins over BF.sub.3 promoted by an ether mixed with a halo alkane diluent at a temperature from -30.degree. to 100.degree. C. to produce oligomers suitable for drying oils. Alpha olefins having from 5 to 20 carbon atoms are oligomerized using BF.sub.3 plus an alcohol or water promoter as described in U.S. Pat. No. 3,382,291 to Brennan. In this patent, BF.sub.3 and a mixture of BF.sub.3 plus the promoter complex are introduced in two separate streams. Another U.S. Pat. by Brennan, No. 3,742,082, concerns the dimerization of alpha olefins via BF.sub.3 which is promoted with phosphoric acid or water at a temperature from 100.degree. to 150.degree. C. U.S. Pat. No. 3,763,244 to Shubkin, which describes the oligomerization of n-alpha olefins having 6 to 16 carbon atoms over BF.sub.3 promoted with water, at a temperature between 10.degree. and 60.degree. C. where it is preferred that BF.sub.3 is added continuously.
Yet another U.S. Pat. to Brennan, No. 3,769,363, describes the oligomerization of olefins having 6 to 12 carbon atoms using BF.sub.3 with a carboxylic acid promoter having at least 3 carbon atoms at a temperature between 0.degree. and 20.degree. C. to produce olefins heavy in trimer form. U.S. Pat. No. 3,780,128 also to Shubkin relates to the oligomerization of alpha olefins having 6 to 16 carbon atoms in which BF.sub.3 is employed in a molar excess of alcohol. U.S. Pat. No. 3,876,720 to Heilman, et al. describes a two-step procedure by which alpha olefins having 8 to 12 carbon atoms are converted to vinylidene olefins which are then reacted over a 1:1 molar complex of BF.sub.3 and alcohol to produce oligomerized vinylidene olefins. A method for oligomerizing both short and long chain alpha olefins having from 14 to 20 carbon atoms simultaneously over BF.sub.3 with an alcohol or water promoter at 0.degree. to 60.degree. C. with a monomer recycle is described in U.S. Pat. No. 4,225,739 to Nipe, et al. There is also U.S. Pat. No. 4,263,465 to Sheng, et al. which describes a two-step process for reacting one-butene with a higher alpha olefin over BF.sub.3 in the presence of a proton donor at a temperature from -30.degree. to 50.degree. C. to produce an oligomer having 8 to 18 carbon atoms. The intermediate oligomer is reacted with other higher alpha mono olefins over the same catalyst system from -30.degree. to 60.degree. C. to produce oligomers having 20 to 40 carbon atoms. For more information on BF.sub.3 -catalyzed oligomerization of alpha olefins, see Brennan, "Wide-Temperature Range Synthetic Hydrocarbon Fluids," Ind. Eng. Chem. Prod. Res. Dev. 1980, Vol. 19, pp 2-6 and Shubkin, et al., "Olefin Oligomer Synthetic Lubricants: Structure and Mechanism of Formation," Ind. Eng. Chem. Prod. Res. Dev. 1980, Vol. 19, pp 15-19.
Two patents have been located which involve the reaction of internal olefins over Friedel-Crafts catalysts. U.S. Pat. No. 4,167,534 to Petrillo, et al. describes olefins which are both alpha and internal having from 10 to 15 carbon atoms which are reacted over Friedel-Crafts catalysts between 20.degree. and 200.degree. C. to produce oligomers. The catalysts used in the examples of this patent are only AlCl.sub.3 and NaAlCl.sub.4. The internal olefins are also those that are statistically distributed. Also, the oligomers found useful therein seem to be the hydrogenated bottoms product after the unreacted olefins are removed, without further distillation. U.S. Pat. No. 4,218,330 to Shubkin describes hydrogenated dimers from alpha olefins having from 12 to 18 carbon atoms, especially 1-tetradecene, made using a Friedel-Crafts catalyst, which includes therein boron trifluoride with a promoter. Shubkin's method uses predominantly alpha olefins, although the specification mentions that "fairly large amounts of internal olefins can be tolerated without adversely affecting the physical properties of the oligomer." This last remark from Shubkin reveals the general feeling of those working in the field that internal olefins do not produce oligomers with good properties for synthetic lubricants. For example, in U.S. Pat. No. 3,952,071 to Isa, et al., it is revealed that olefins may be oligomerized in the presence of a mixture of a polyhydric alcohol derivative and an aluminum halide. Isa, et al. mention that the olefin could be internal or alpha although alpha olefins are the only ones used in the examples therein. U.S. Pat. No. 3,947,509, also to Isa, et al., also claims that internal olefins may be used over a ketone and ester ether or alcohol promoted aluminum chloride catalyst although only alpha olefins are used in the examples.
U.S. Pat. No. 4,300,006 was issued on November 10, 1981. It describes a process for producing a hydrocarbon oil by contacting a mixture of alpha and at least 50 weight percent internal olefins with a boron trifluoride dimerization catalyst. However, the productivity of useful products from the process revealed in U.S. Pat. No. 4,300,006 is quite low. For example, an alkane diluent is found to be necessary in the process described therein which, in addition to distilling out the lights and the heavies to obtain the lube oil, results in little useful product. Further, this method requires a much longer reaction time and a higher catalyst concentration than desired. It would be beneficial if a method for producing synthetic lubricant components could be devised which would overcome the aforementioned disadvantages.
In the field of oligomerizing olefins for synthetic lubricants, it is a continual problem to produce olefins having low viscosities at room temperature and below but which have a high viscosity index and low volatility.